Polyimide-based resins are excellent in heat resistance, electric insulation, solvent resistance, and mechanical stability, so that they have been conventionally used in various fields.
Particularly, in the electric and electronic material field, a cured film produced from a photosensitive polyhydroxyimide-based resin in which photosensitive properties are imparted by introducing a hydroxy group into a polyimide is found to have not only the above properties of a polyimide-based resin, but also a high resolution or a high sensitivity, so that the application of the cured film is enlarged and the cured film starts to spread into not only the semiconductor field, but also the display field.
For example, there is described a positive photosensitive resin composition using a polyhydroxyimide as a material capable of obtaining a positive pattern having a high resolution, a high sensitivity, and an advantageous size controlling property.
It is considered that the polyhydroxyimide can be produced, for example, by the same method as a production method of a polyimide. That is, there is first conceived a method for obtaining an imide by reacting a tetracarboxylic dianhydride and a diamine as monomers to synthesize a polyamic acid that is an imide precursor and then by cyclizing the polyamic acid either by (a) heating the polyamic acid to dehydrate the polyamic acid (thermal imidation method) or by (b) using a dehydrocondensing agent or a ring closing catalyst (chemical imidation method).
In the production of a polyimide by (a) the thermal imidation method, there is adopted a method in which a heating-dehydration reaction is effected by using an acid catalyst or an azeotropic solvent as an assistant for an imidation reaction to imidate the polyamic acid. At this time, generally, the polyamic acid is heated to a temperature of 180° C. to 250° C. to effect the reaction.
In the production of a polyimide by (b) the chemical imidation method, there is adopted a method in which a dehydrocondensing agent and a ring closing catalyst are directly added to a polyamic acid solution and the resultant mixture is heated and dried. As the dehydrocondensing agent, a carboxylic anhydride such as acetic anhydride, propionic anhydride, and benzoic anhydride or DCC (dicyclohexylcarbodiimide) is utilized. As the ring closing catalyst, an aliphatic tertiary amine such as triethylamine, heterocyclic tertiary amine such as isoquinoline, pyridine, β-picoline, aminopyridine, and imidazole, or the like is utilized, particularly, an acetic anhydride-pyridine-based ring closing catalyst is widely used (for example, Patent Document 1).
However, when (b) the chemical imidation method is applied to the production of a polyhydroxyimide, even a hydroxy group in a side chain of a polyamic acid is reacted with a large amount of acetic anhydride existing in the reaction system to be converted into an acetoxy group, so that when (b) the chemical imidation method is applied to a photosensitive resin composition or the like, there is the problem that a necessary developing group (hydroxy group) becomes inactivated.
Therefore, as the method for producing a polyhydroxyimide without inactivating a hydroxy group, there is described a method applying (a) the thermal imidation method, for example, a method for performing the imidation including: synthesizing an imide precursor in N-methyl-2-pyrrolidone (NMP); then adding an aromatic hydrocarbon solvent (such as m-xylene) that can be subjected to azeotropy with water as a dehydrating agent to the imide precursor; and heating the resultant mixture at 180° C. to subject the imide precursor to a dehydration reaction (Patent Document 2).
Or, as another method, there is also described, for example, a method for directly producing a polyhydroxyimide by heating an acid dianhydride and a diamine at a high temperature (180° C.) in a solvent mixture of an aprotic polar solvent (such as NMP) and a dehydration solvent (such as toluene) in the presence of an acid catalyst (γ-valerolactone) and a base (pyridine) to progress the reaction while subjecting a water content to azeotropy to remove the water content (Patent Document 3).